In general, the invention relates to performing adaptations between protocols in digital wireless data transmission systems. In particular, the invention relates to performing adaptations in a system where the mobile station may, through a given generally defined radio access network, use the services offered by several different core networks. Here the term wireless means that the mobile stations can be freely movable, and that they have a wireless connection to the base stations of the system.
Functions applying digital data transmission protocols are usually described as a stack according to the OSI (Open Systems Interface) model, where the tasks of the various layers of the stack, as well as data transmission between the layers, are exactly defined. In the GSM (Global System for Mobile telecommunications) system, which in this patent application is observed as an example of a digital wireless data transmission system, there are defined five operational layers. The lowest is the transmission layer, and on top of it, there are located in the following order: the RR (Radio Resource management) layer, the MM (Mobility Management) layer, the CM (Communication Management) layer and the OAM (Operation, Administration and Maintenance) layer. The last mentioned OAM layer is not necessarily always located conceptually in the same protocol stack with the rest, because it does not directly increase the value of the service that the user obtains from the other layers. The base station subsystem (BSS) formed by base transceiver stations (BTS) and base station controllers (BSC) operates mainly on the transmission and RR layers, whereas the mobile station (MS) and the mobile services switching centre (MSC) in their operation implement the layers from the transmission layer up to the CM layer. The operation of the home location register (HLR) is concentrated on the MM layer and the CM layer, and the gateway MSC (GMSC) operates on the CM layer only.
Along with the development of digital wireless data transmission systems, there is created a situation where it is advantageous for the mobile station to be able to utilise the services offered by several different core networks (CN). In this new situation, the entity formed by the base station subsystems is called a radio access network (RAN), and the core networks are formed of various central systems which can, in addition to versatile data transmission possibilities, offer various smart network services, such as automatic data transmission, map and location information, banking and purchase services, entertainment, etc. FIG. 1 is a schematical illustration of a suggestion for a third-generation digital cellular radio system, where in between the mobile stations 100 and core networks 101, 102 and 103, there may operate one or several radio access networks 104, 105 and 106. Through a given radio access network, the mobile station 100 can be connected to several core networks, for example like in the drawing, via the radio access network 104 to the core network 101 or 102, and respectively the connection between the mobile station and a given core network can take place through more than one radio access network, for example like in the drawing the connection between the mobile station 100 and the and the core network 102 via the radio access network 104 or 105. The radio access network 104, which is not available to one core network only, is called a generic radio access network (GRAN) or UTRA (UMTS Terrestrial Radio Access; Universal Mobile Telecommunications System).
In a situation according to FIG. 1, problems are connected to data transmission between the different protocol layers. Relations between the protocol layers are illustrated in FIG. 2. The lowest protocol layer between the mobile station MS and the base station subsystem of the generic radio access network UTRA BSS is the layer 1 (L1) 200, 201, which corresponds to a physical radio connection. Above it, there is located an entity corresponding to the layers 2 and 3 or a regular OSI model, wherein the lowest layer is a radio link control/media access control (RLC/MAC) layer 202, 203; on top of it a logical link control (LLC) layer 204, 205; and topmost a radio resource control (RRC) layer 206, 207. Between the base station subsystem UTRA BSS of the generic radio access network and an interworking unit/core network IWU/CN located in the core network, there is assumed to be applied a so-called Iu interface, where the layers corresponding to the above described layers from L1 to LLC are the layers L1 and L2 of the OSI model (blocks 208 and 209 in the drawing), and the layer corresponding to the above described RRC layer is the layer L3 of the OSI model (blocks 210 and 211 in the drawing).
The mobile station MS must include a higher-level control protocol 212 and a protocol 213 for serving higher-level users, of which the former communicates with the RRC layer 206 in order to realise control functions connected to data transmission connections, and the latter communicates directly with the LLC layer 204 in order to transmit such data that directly serves the user (for instance digitally encoded speech). In a mobile station of the GSM system, the blocks 212 and 213 are included in the above mentioned MM layer.
The services offered by core networks may contain remarkable differences. If the mobile station MS must be able to utilise several different core networks, it must contain various higher protocol layers 212 and 213 dependent on the core network applications, according to the core network that it communicates with at each point of time. The core networks are continuously being developed further, wherefore the capabilities and operations of the protocol layers 212 and 213 must be adjustable. On the other hand, there already exist complete second-generation core networks, wherefore it would be advantageous if the mobile station could utilise the services of a second-generation connection irrespective of the fact that the radio access network belongs to the third generation.
The object of the present invention is to introduce a method and a system whereby the mobile station can utilise the services offered by different core networks through the interworking of a third-generation radio access network.
The objects of the invention are achieved by providing the mobile station with an adaptation layer located on top of the LLC and RRC layers; said adaptation layer has a standardised interface in the downwardly direction, and it performs two-way mapping in between the primitives used by the layers located on top of it, and the primitives of the LLC and RRC layers. Here the term primitive refers to the basic messages between the protocol layers.
The method according to the invention is characterised in that the mobile station deals with messages according to the first protocol on certain lower protocol layers, and with messages according to the second protocol on a certain higher protocol layer, so that on the adaptation layer located in between the higher and the lower protocol layers, there is carried out an adaptation where the messages according to the first and second protocol are mapped to correspond to each other.
The invention also relates to a mobile station characterised in that it comprises, in said protocol stack, lower protocol layers according to a given first protocol, and a higher protocol layer according to a given second protocol, and in between them an adaptation layer for performing such a two-way adaptation where the messages according to the first and second protocol are mapped to correspond to each other.
In between a generic radio access network and a mobile station, the connections are realised as radio bearer services, and one particular mobile station may have several simultaneous radio bearer services. A third-generation system is characterised in that radio bearer services between one mobile station and base transceiver station can be established and released irrespective of each other. Moreover, each radio bearer service has certain typical properties, such as bitrate, quality of service and direction of data transmission. The adaptation layer according to the invention maps the needs of the higher protocol layers and the possibilities offered by the third-generation radio access network in relation to each other according to the following principles:
Service access points (SAP) are realised in between the adaptation layer and the higher protocol layers; they are not needed in between the adaptation layer and the protocol layers of the radio access network.
The adaptation layer serves in two directions, mapping the primitives of the higher protocol layers into primitives of the radio access network, and vice versa; thus the protocol layers of the radio access network may receive requests from the higher protocol layers and send them responses and messages.
The adaptation layer may maintain a list of active radio bearer services between the mobile station and the radio access network.
The adaptation layer does not have a particular peer entity on the network side, but the respective actions are realised as part of the connection between the radio access network and the core network.
Owing to the adaptation layer, a third-generation radio access network is transparent from the point of view of the higher protocol layers of the second generation.
The adaptation layer includes the necessary smart functions in order to start the radio bearer services and processes typical of the radio access network, in correspondence to the needs of the higher protocol layers in question.
The adaptation layer may receive from the radio access network such additional information which is not directly available for the second-generation higher protocol layers, but which for example prevents the mobile station from requesting a connection that is for capacity reasons not possible in the present cell.
The adaptation layer may include an interface through which it is possible to select and change the core network protocols supported by the mobile station.